Case of the Month
Section Editor: Nicholas Stence, MD
Children's Hospital Colorado, Aurora, CO
October 2021
Next Case of the Month Coming November 9...
Cerebral Fat Embolism
- Background:
- Fat embolism syndrome is defined as an uncommon, life-threatening disease process consisting of pulmonary, CNS, and cutaneous manifestations. It was first described in a German book on normal and pathologic anatomy of the lungs by FA Zenker as a grave complication of long bone fracture.
- It is the result of mechanical obstruction of arterial circulation by neutral fat and is followed by an extensive delayed biochemical toxic injury caused by free fatty acids. Following a fracture of a long bone, a substantial amount of marrow fat is poured into the venous circulation, which then reaches the pulmonary circulation. This fat in the presence of a right-to-left shunt enters the systemic circulation and causes CNS, renal, retinal, and cutaneous manifestations. However, most reported cases of cerebral embolism did not have any right to left. It was seen in a few studies that fat microdroplets smaller than 5 micrometers in size can pass through the pulmonary capillary bed and lead to systemic embolism.
- An alternate opinion is that fat embolism results from a biochemical process that is inflammatory in nature. The inflammatory mediator lipoprotein lipase hydrolyzes fat droplets to free fatty acids in the pulmonary circulation. This leads to a change in homeostasis and fat droplet aggregation in the systemic microvasculature. These emboli exacerbate the development of organ dysfunction. Free fatty acids, being toxic to the lungs and brain, may induce cerebral cytotoxicity.
- Clinical Presentation:
- Respiratory symptoms like tachypnea, dyspnea, and hypoxia are common, and pulmonary failure is seen in 10%.
- Cutaneous manifestations include a reddish-brown petechial rash on the neck, chest, and arms, appearing within 12–36 hours.
- Exudates, cotton-wool spots, edema, hemorrhage, or intravascular fat globules are the most reported retinal changes.
- Other nonspecific changes seen are thrombocytopenia, jaundice, elevated erythrocyte sedimentation rate, anemia, lipuria, fat macroglobulinemia, tachycardia, and pyrexia.
- Neurologic symptoms in cerebral fat embolism are widely variable, ranging from headache, confusion, and seizure to coma. Coexisting brain contusion or hypoxic-ischemic injury caused by trauma can further complicate the clinical scenario and make diagnosis of this condition difficult. The respiratory presentations, on the other hand, are quite characteristic.
- Gurd and Wilson’s criteria are widely used for diagnosis. Major criteria include hypoxia, deteriorating mental status, and petechiae. Minor criteria consist of tachycardia, fever, anemia, and thrombocytopenia.
- Key Diagnostic Features:
- Despite the diagnosis of cerebral fat embolism being majorly a clinical one, neuroimaging plays an important part. CT scans of the brain in such patients are often normal and MRI is the workhorse of diagnosis.
- Analysis of MR images shows that patterns of involvement evolve with time and can be categorized into 2 major types. The type 2 pattern could be further divided into 3 subtypes.
- Type 1 (scattered cytotoxic edema): Also known as the “starfield” pattern as coined by Parizel et al in 2001, it is the most common pattern. Scattered spot lesions with restricted diffusion on DWI are seen distributed bilaterally in watershed zones and deep gray matter, such as the centrum semiovale, basal ganglia, and thalami. The signal of T2WI may be isointense or hyperintense.
- Type 2A (confluent cytotoxic edema in white matter): Confluent symmetric lesions with restricted diffusion are seen on DWI in periventricular and subcortical white matter bilaterally. The cerebellar peduncles, corpus callosum, and posterior internal capsule may be involved. On T2WI, lesions may be faintly hyperintense or without any signal abnormality.
- Type 2B (vasogenic edema lesions that may enhance): Typically seen in the subacute stage, this type of lesion appears hyperintense on T2WI in both gray and white matter and shows increased diffusivity, unlike the previous 2 stages.
- Type 2C (petechial hemorrhage of white matter): These lesions have the same distribution pattern as type 2A and are better appreciated on SWI than GRE images.
- Type 3 (chronic sequelae): Incomplete lesion resolution rather than a true recovery is common with atrophy of brain parenchyma. The lesions are hyperintense on T2WI without restricted diffusion and may represent sequelae of infarction, cavitation, scar formation, gliosis, or chronic demyelination.
- Differential Diagnoses:
- Diffuse axonal injury (DAI): Although it presents as petechial hemorrhage, DAI typically involves the gray-white matter interface of the frontotemporal lobes and corpus callosum. Cerebral fat embolism petechial hemorrhage, on the other hand, is predominantly in the white matter. Severe grades of DAI involve the brainstem, and involvement of the cerebellum is rare. Involvement of the cerebellum with relative sparing of the brainstem in our case makes cerebral fat embolism a more likely diagnosis.
- Treatment:
- ​Supportive care is the mainstay of treatment for fat embolism syndrome.
- Clofibrate, dextran-40, ethyl alcohol, heparin, aspirin, and steroids have been used in the past without much of a positive outcome.
- Early splinting and fixation of orthopedic fractures in trauma patients is recommended for prevention.
- Decreased manipulation of intramedullary fat leads to a lower incidence of fat embolism.